1. Field of the Invention
The present invention relates to a rechargeable battery.
2. Description of the Related Art
Rechargeable batteries can be repeatedly charged and discharged unlike primary batteries which cannot be repeatedly charged. A low-capacity rechargeable battery constituting one cell is used for a small portable electronic device, i.e., a mobile phone, a laptop computer, or a camcorder. A large-capacity rechargeable battery constituting a plurality of cells connected to each other in a pack type is widely used for a power supply for driving a motor in a hybrid electric vehicle, etc.
Rechargeable batteries are manufactured in various shapes. Exemplary shapes may include a cylindrical shape, a quadrangular shape, etc.
Rechargeable batteries which are coupled with each other in series to be used for driving a motor in an electric vehicle, etc. that requires high power may constitute a large-capacity rechargeable battery module.
As the rechargeable battery is repetitively charged and discharged, an electrode assembly is repetitively expanded and contracted. As a result, the stress between the electrode assembly and a case and between the electrode assembly and a core around which the electrode assembly is wound increases. Since a space is provided between the case and the electrode assembly, the stress can be absorbed to some degree even though the stress is generated, but since the space between the electrode assembly and the core is narrow, a comparatively large stress is generated. Of course, when the electrode assembly is excessively expanded, the stress gradually increases between the electrode assembly and the case.
When the stress is concentrated on the electrode assembly, the electrode assembly is pressed, thus, the electrolyte solution remaining in the electrode assembly moves outside of the electrode assembly. Therefore, charge efficiency and heat radiation efficiency are deteriorated and the output of the rechargeable battery is reduced. These problems can become fatal defects in evaluating the lifespan and performance of the high-output rechargeable battery.
Further, a rechargeable battery used in an electric vehicle (EV) or a hybrid electric vehicle (HEV) performs rapid charging and discharging operations. It is most important that the output of the rechargeable battery is not deteriorated even at the time of performing a rapid charging and discharging operation. However, when the charging and discharging operations are rapidly performed, the electrode assembly is expanded more rapidly as described above, such that the output is remarkably reduced. The problem occurs because the stress between the electrode assembly and the core increase. The lifespan of a portion on which the stress is concentrated is deteriorated, such that the lifespan of the rechargeable battery is reduced. Further, when the stress is not alleviated, the separator is pressed, such that the separator cannot normally transfer ions. As a result, the output of the rechargeable battery is lowered.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.